Searched a lot on the net, but not all questions are answered. I'm looking for an external audio unit for my GH4.

I'm looking for a unit which does the following:
- Two or four XLR inputs, phantom power
- Record on sd card as back up
- Monitor via headphone one audio source at a time not the whole mix
- Output in case of two sources to camera dual mono (not stereo)
- Start stop the recording remote by camera start stop (is this possible?)

How much you looking to spend?
On the low cost side and based on your desired criteria, your choices are few.. especially concerning the ability to 'solo' and has a secondary mirror drive... The 'new' Zoom F8 may be worth looking into, which supports two SD cards and can solo tracks... But it's a 'Zoom'.. which are of infamous quality. (low) According to 1st reports, the F8 allegedly sounds decent and of solid build.. reliability is unknown at this point.. Shipping of actual units just commenced a week or so ago.